Remote unit for communicating with base stations and terminal devices

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This is a continuation of U.S. patent application Ser. No. 14/213,168, filed Mar. 14, 2014 and titled “Remote Unit for Communicating with Base Stations and Terminal Devices,” which claims priority to U.S. Provisional Application Ser. No. 61/790,515 filed Mar. 15, 2013 and titled “Remote Antenna Unit for Communicating with Base Stations and Mobile Communication Devices,” the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

0002The present disclosure relates generally to telecommunications systems and more particularly (although not necessarily exclusively) to remote units of distributed antenna systems that can communicate with base stations and terminal devices.

BACKGROUND

0003A distributed antenna system (“DAS”) may include master units and remote units. Master units may be connected to base stations. Master units receive downlink signals from base station and distribute downlink signals in analog or digital format to multiple remote units. The remote units transmit downlink signals to terminal devices within coverage areas serviced by the remote units. In the uplink direction, signals from terminal devices may be received by the remote units. The remote units may combine uplink signals and transmit the combined uplink signals to master units. Master units may transmit uplink signals to the serving base stations.

SUMMARY

0004Certain aspects and features of the present invention are directed to distributed antenna systems in which remote units can communicate with base stations and terminal devices.

0005In one aspect, a distributed antenna system is provided. The distributed antenna system can include a master unit that is communicatively coupled to a first remote unit and a second remote unit. The first remote unit can communicate RF signals between the master unit and a terminal device. The first remote unit can also receive analog downlink RF signals from a base station and convert the analog downlink RF signals to digital downlink signals. The first remote unit can provide the digital downlink signals to the master unit. The master unit can transmit the digital downlink signals received from the first remote unit to the second remote unit.

0006In another aspect, a remote unit of a distributed antenna system is provided. The remote unit can include a signal processing module and a transceiver. The transceiver can communicate RF signals between a master unit of the distributed antenna system and a terminal device. The transceiver can also receive analog downlink RF signals from a base station. The signal processing module can convert the analog downlink RF signals to digital downlink signals and provide the digital downlink signals to the master unit.

0007In another aspect, a distributed antenna system for providing device-to-device communication is provided. The distributed antenna system can include a first remote unit, a second remote unit, and a master unit that is communicatively coupled to the first and second remote units. The first remote unit can receive a signal from a first terminal device. The master unit can receive the signal from the first remote unit and provide the signal to the second remote unit for transmission to the second terminal device. The second remote unit can transmit the signal to a second terminal device.

0008These illustrative aspects and features are mentioned not to limit or define the disclosure, but to provide examples to aid understanding of the concepts disclosed in this application. Other aspects, advantages, and features of the present disclosure will become apparent after review of the entire application.

BRIEF DESCRIPTION OF THE DRAWINGS

<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram depicting an example of a distributed antenna system that can include a donor remote unit for communicating with base stations according to one aspect of the present disclosure.

<figref idref="DRAWINGS">FIG. 2</figref> is a block diagram depicting the donor remote unit of <figref idref="DRAWINGS">FIG. 1</figref> according to one aspect of the present disclosure.

<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram depicting an example of the donor remote unit of <figref idref="DRAWINGS">FIG. 2</figref> with multiple duplexers according to one aspect of the present disclosure.

<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram depicting an alternative example of the donor remote unit of <figref idref="DRAWINGS">FIG. 2</figref> with a configurable isolation sub-system for communicating in different frequency bands according to one aspect.

<figref idref="DRAWINGS">FIG. 5</figref> is a flow chart depicting a process for using the donor remote unit of <figref idref="DRAWINGS">FIG. 1</figref> to compensate for a base station malfunction according to one aspect of the present disclosure.

<figref idref="DRAWINGS">FIG. 6</figref> is a block diagram depicting a remote unit configured for device-to-device communication according to one aspect of the present disclosure.

DETAILED DESCRIPTION

0015A remote unit of a distributed antenna system (“DAS”) is disclosed that can communicate RF signals with base stations in addition to communicating RF signals with terminal devices in a coverage zone serviced by the remote unit. In some aspects, a master unit can route signals received from the remote unit to other remote units for transmission to terminal devices.

0016In accordance with some aspects, a donor remote unit can receive both uplink signals from terminal devices and downlink signals from base stations. The donor remote unit can transmit downlink signals received from base stations to a master unit for distribution via the DAS. The donor remote unit can also receive downlink signals from a master unit and transmit the downlink signals to terminal devices in a coverage zone serviced by the donor remote unit. In some aspects, the donor remote unit can also transmit the signals received from a base station to other remote units for transmission to terminal devices in other coverage zones serviced by the other remote units.

0017As used herein, the term “donor remote unit” can refer to any remote unit that can include or be communicatively coupled to one or more antennas and that can be configured to wirelessly receive downlink signals from a base station and to wirelessly receive uplink signals from terminal devices. For example, a donor remote unit can include a transceiver that is tuned for wirelessly receiving downlink signals in a frequency band used by a base station. The donor remote unit can provide an RF link between the DAS and another base station in addition to the base stations in communication with the master unit of the DAS. For example, a donor remote unit can receive signals in an analog RF format from a base station and provide signals in a digital format to one or more devices in the DAS via a direct connection. For cases in which few terminal devices are served by an operator within a coverage area of the DAS, a donor remote unit can provide an RF link to a macrocell serviced by a base station in or near the coverage area of the DAS. The RF link provided by the donor remote unit can reduce or eliminate costs associated with installing additional base stations to service a smaller number of terminal devices.

0018As used herein, the term “terminal device” can refer to an electronic device used to communicate voice and/or data via a telecommunications system, such as (but not limited to) a small cell network or other cellular network. Other terminology used to refer to terminal devices and non-limiting examples of such devices can include mobile stations, mobile devices, access terminals, subscriber stations, terminal mobile terminals, remote stations, user terminals, terminals, subscriber units, cellular phones, smart phones, personal digital assistants (“PDAs”), laptop computers, netbooks, e-readers, wireless modems, etc.

0019The RF link provided by the donor remote unit can reduce or eliminate the need to use a separate RF repeater to receive signals from a nearby macrocell and transmit the received signals to the DAS. A donor remote unit may be smaller than a repeater unit. The smaller size of a donor remote unit may allow the donor remote unit to be more easily positioned in different coverage areas than a repeater.

0020In additional or alternative aspects, remote units for a DAS can be configured for device-to-device communication between terminal devices in a coverage area serviced by the DAS. A master unit or other unit in the DAS can receive signals within a defined bandwidth from multiple remote units. The level of the signals within the bandwidth can be compared with a threshold signal level. Signals having a signal level above the threshold signal level can be summed or otherwise combined. The combined signals can be routed to remote units whose signal level is below the threshold. The combined signal can be transmitted by the remote units. In some aspects, a frequency shift can be applied to the combined signal prior to transmission by the remote units.

0021As used herein, the term “device-to-device communication” can refer to a mode of communication between or among terminal devices that communicate via a DAS in which the signal traffic from one terminal device to another terminal device does not pass through a centralized base station or other device in the telecommunication system. Signal traffic can include voice communications or data communications intended for consumption by a user of a terminal device. Device-to-device communication may be implemented in a DAS by receiving signals from a first terminal device at a first remote unit, providing the received signals to a second remote unit via a master unit or extension unit, and transmitting the signals from the second remote unit to a second terminal device.

0022Detailed descriptions of certain examples are discussed below. These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional aspects and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative examples but, like the illustrative examples, should not be used to limit the present disclosure.

0023<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram depicting an example of a DAS <b>100</b> that can include a donor remote unit <b>104</b> for communicating with base stations according to one aspect.

0024The DAS <b>100</b> can include a master unit <b>102</b>, an extension unit <b>103</b>, a donor remote unit <b>104</b>, and remote units <b>106</b><i>a</i>, <b>106</b><i>b</i>. The donor remote unit <b>104</b> and remote units <b>106</b><i>a</i>, <b>106</b><i>b </i>can provide signal coverage to terminal devices positioned in respective coverage zones <b>108</b>, <b>110</b>, and <b>112</b>.

0025The master unit <b>102</b> can receive downlink signals from a base station <b>114</b> and transmit uplink signals to the base station <b>114</b>. Any suitable communication link can be used for communication between the base station <b>114</b> and the master unit <b>102</b>, such as (but not limited to) a direct connection or a wireless connection. A direct connection can include, for example, a connection via a copper, optical fiber, or other suitable communication medium. In some aspects, the master unit <b>102</b> can include an external repeater or internal RF transceiver included on a donor card to communicate with the base stations. In some aspects, the master unit <b>102</b> can combine downlink signals received from different base stations <b>114</b>. The master unit <b>102</b> can transmit the combined downlink signals to one or more of the donor remote unit <b>104</b> and the remote units <b>106</b><i>a</i>, <b>106</b><i>b. </i>

0026In some aspects, the master unit <b>102</b> can be connected to remote units via one or more extension units or other intermediate devices. For example, <figref idref="DRAWINGS">FIG. 1</figref> depicts a master unit <b>102</b> that is communicatively coupled to an extension unit <b>103</b>. The extension unit <b>103</b> is communicatively coupled to the donor remote unit <b>104</b> and the remote unit <b>106</b><i>a</i>. In additional or alternative aspects, the master unit <b>102</b> can be connected to remote units directly without using extension units or other intermediate devices. For example, <figref idref="DRAWINGS">FIG. 1</figref> depicts a master unit <b>102</b> that is communicatively coupled to a remote unit <b>106</b><i>b </i>without using an extension unit.

0027The donor remote unit <b>104</b> and the remote units <b>106</b><i>a</i>, <b>106</b><i>b </i>can provide signal coverage in coverage zones <b>108</b>, <b>110</b>, <b>112</b> by transmitting downlink signals to terminal devices and receiving uplink signals from the terminal devices. The donor remote unit <b>104</b> and the remote units <b>106</b><i>a</i>, <b>106</b><i>b </i>can transmit uplink signals to the master unit <b>102</b>. The master unit <b>102</b> can combine uplink signals received from the donor remote unit <b>104</b> and the remote units <b>106</b><i>a</i>, <b>106</b><i>b </i>for transmission to the base station <b>114</b>.

0028For illustrative purposes, <figref idref="DRAWINGS">FIG. 1</figref> depicts a DAS <b>100</b> that communicates with two base stations <b>114</b>, <b>116</b> and that includes a single master unit <b>102</b>, a single extension unit <b>103</b>, a single donor remote unit <b>104</b>, and two remote units <b>106</b><i>a</i>, <b>106</b><i>b</i>. However, a DAS <b>100</b> can communicate with any number of base stations and can include any suitable number of master units <b>102</b>, extension units <b>103</b>, donor remote units <b>104</b>, and remote units <b>106</b><i>a</i>, <b>106</b><i>b</i>. In some aspects, a DAS <b>100</b> can omit one or more of the extension unit <b>103</b> or the remote units <b>106</b><i>a</i>, <b>106</b><i>b. </i>

0029The donor remote unit <b>104</b> can communicate with both the master unit <b>102</b> (via the extension unit <b>103</b>) and a base station <b>116</b> within a transmission range of the coverage zone <b>108</b>. For example, the donor remote unit <b>104</b> can receive downlink RF signals from the base station <b>116</b> and transmit uplink RF signals to the base station <b>116</b>. Communicating RF signals with the base station <b>116</b> can allow the donor remote unit <b>104</b> to operate as an RF donor pickup transceiver in addition to a mobile-side transceiver. The donor remote unit <b>104</b> can communicate downlink signals received from the base station <b>116</b> to the master unit <b>102</b>.

0030The master unit <b>102</b> can combine the downlink signals received from the donor remote unit <b>104</b> with downlink signals in the same frequency band received from other base stations. The master unit <b>102</b> can communicate the combined downlink signal to one or more of the other remote units <b>106</b><i>a</i>, <b>106</b><i>b</i>. The downlink signal can be transmitted by the other remote units <b>106</b><i>a</i>, <b>106</b><i>b. </i>

0031In a non-limiting example, the DAS <b>100</b> depicted in <figref idref="DRAWINGS">FIG. 1</figref> can be used to provide signal coverage for a coverage area serviced by multiple base stations <b>114</b> in communication with the master unit <b>102</b> and a neighboring base station <b>116</b> (such as, but not limited to, a macrocell base station) in communication with the donor remote unit <b>104</b>. A first base station <b>114</b> that is communicatively coupled to the master unit <b>102</b> may operate in the sub-band A of frequency band <b>1</b>. A second base station <b>114</b> that is communicatively coupled to the master unit <b>102</b> may operate in the sub-band B of frequency band <b>1</b>. A third base station <b>114</b> that is communicatively coupled to the master unit <b>102</b> may operate in the sub-band C of frequency band <b>2</b>. The macrocell base station <b>116</b> may operate in the sub-band D of frequency band <b>2</b>. The master unit <b>102</b> can combine signals received from the first and second base stations <b>114</b> into a single signal in frequency band <b>1</b>. The combined signal in frequency band <b>1</b> can include the sub-bands A and B. The master unit <b>102</b> can transmit the combined signal having frequencies in the sub-bands A and B of frequency band <b>1</b> to remote units <b>106</b><i>a</i>, <b>106</b><i>b </i>in the respective coverage zones <b>110</b>, <b>112</b> of the DAS <b>100</b>.

0032The donor remote unit <b>104</b> can receive signals in frequency band <b>2</b>. The donor remote unit <b>104</b> can isolate signals in a sub-band D of frequency band <b>2</b> by applying a bandpass filter that attenuates signals having frequencies outside of the sub-band D. The donor remote unit <b>104</b> can transmit the signals in the sub-band D to the master unit <b>102</b> via the extension unit <b>103</b>. The master unit <b>102</b> can combine signals in the sub-band C of frequency band <b>2</b> received from the third base station <b>114</b> with signals in the sub-band D received from the macrocell base station via the donor remote unit <b>104</b>. The master unit <b>102</b> can transmit the combined signal having frequencies in the sub-bands C and D of frequency band <b>2</b> to remote units <b>106</b><i>a</i>, <b>106</b><i>b</i>. The master unit <b>102</b> can also transmit signals having frequencies in the sub-band C of frequency band <b>2</b> to the donor remote unit <b>104</b> for transmission to terminal devices.

0033<figref idref="DRAWINGS">FIG. 2</figref> is a block diagram depicting an example of the donor remote unit <b>104</b> according to one aspect. The donor remote unit <b>104</b> can include a transceiver <b>202</b>, a processor <b>204</b>, and an signal processing module <b>208</b>.

0034The transceiver <b>202</b> can be configured to receive downlink RF signals from a base station and transmit uplink RF signals to the base station. In some aspects, the transceiver <b>202</b> can be tuned to different frequencies based on command signals received from the processor <b>204</b>.

0035The processor <b>204</b> can include any device suitable for executing program instructions to control operation of the donor remote unit <b>104</b>. Examples of processor <b>204</b> include a microprocessor, an application-specific integrated circuit (“ASIC”), a field-programmable gate array (“FPGA”), or other suitable processor. The processor <b>204</b> may include one processor or any number of processors.

0036The donor remote unit <b>104</b> can communicate with the master unit <b>102</b> via any suitable signal processing module <b>208</b>, such as (but not limited to) a physical layer transceiver or other suitable component configured for communicating with a master unit <b>102</b>. The signal processing module <b>208</b> can process uplink and downlink signals for communication with the master unit <b>102</b> or extension unit <b>103</b>. The signal processing module <b>208</b> can include one or more digital components or devices, one or more analog components or devices, or any combination thereof for communicating signals between the donor remote unit <b>104</b> and the master unit <b>102</b> or extension unit <b>103</b>. For example, the signal processing module <b>208</b> can include one or more digital signal processors, one or more filters, one or more digital-to-analog converters, one or more analog-to-digital converters, etc. The signal processing module <b>208</b> can convert analog downlink signals received from a base station <b>116</b> into digital downlink signals to be provided from the donor remote unit <b>104</b> to the master unit <b>102</b>.

0037In some aspects, the donor remote unit <b>104</b> can be configured to receive both uplink signal and signals from other base station by using a transceiver <b>202</b> that does not include a duplexer. In some remote units that do not receive RF downlink signals transmitted by base stations, a fixed duplexer may provide isolation between transmit signals in received signals. Using a transceiver <b>202</b> that does not include a duplexer can allow a receiver component of the transceiver <b>202</b> to be tuned to receive signals in any frequency band, including one or more frequency bands used by the base station <b>116</b>.

0038In other aspects, the donor remote unit <b>104</b> can include at least two duplexers. For example, <figref idref="DRAWINGS">FIG. 3</figref> is a block diagram depicting an example of a donor remote unit <b>104</b> that includes multiple duplexers according to one aspect. The donor remote unit depicted in <figref idref="DRAWINGS">FIG. 2</figref> includes a mobile communication duplexer <b>302</b> and a base station communication duplexer <b>304</b>. The mobile communication duplexer <b>302</b> can be used for communication with terminal devices. The mobile communication duplexer <b>302</b> can be configured to provide isolation between analog RF uplink signals received from one or more terminal devices and analog RF downlink signals transmitted to the one or more terminal devices. The base station communication duplexer <b>304</b> can be used for communication with a base station. The base station communication duplexer <b>304</b> can be configured to provide isolation between analog RF downlink signals (e.g. analog downlink RF signals) received from a base station <b>116</b> and other signals transmitted by the donor remote unit <b>104</b> (e.g., analog RF uplink signals transmitted to the base station <b>116</b>, analog RF downlink signals transmitted to terminal devices, etc.).

0039In other aspects, the donor remote unit <b>104</b> can include a configurable isolation sub-system. For example, <figref idref="DRAWINGS">FIG. 4</figref> is a block diagram depicting an alternative example of a donor remote unit <b>104</b> that includes transceiver <b>202</b>′ with a configurable isolation sub-system <b>402</b> for communicating in different frequency bands according to one aspect. The configurable isolation sub-system <b>402</b> can be configured to provide isolation between signals transmitted to terminal devices and signals received from the terminal devices. The configuration of the configurable isolation sub-system <b>402</b> can be modified to allow the donor remote unit <b>104</b> to communicate with one or more neighboring base stations <b>116</b>.

0040In some aspects, the configurable isolation sub-system <b>402</b> can include a single-step configurable filter that can include one or more bandpass filters. The desired downlink frequency band of a single-step configurable filter can be manually selected in a single physical step, such as (but not limited to) using a switch matrix to select a channel corresponding to a particular frequency band on a multi-channel switch filter bank.

0041In additional or alternative aspects, the configurable isolation sub-system <b>402</b> can include an electronically configurable filter. An electronically configurable filter may include one or bandpass filters that can be configured electronically. Configuring the filter can include receiving an electronic control signal and responding to the electronic control signal by changing the frequency response accordingly. The frequency response may be the desired frequency band to be passed. The electronic control signal may be received from an external controller. The electronically configurable filter can include a microprocessor or similar device that can respond to the electronic control signal by configuring the electronically configurable filter to have a desired frequency response. In some aspects, a bandpass filter can include one or more varactor diodes. The frequency response of the bandpass filter can be adjusted by varying the capacitance of one or more varactor diodes in response to the electronic control signal. The capacitance of the varactor diodes can be varied by applying varying input voltages to terminals of the varactor diodes. Altering the capacitance of one or more varactor diodes can alter both the center frequency and bandwidth of the bandpass filter. In some aspects, the source of the applied voltage may be disposed in the electronically configurable filter, with applied voltage levels controlled by the microprocessor in response to an electronic control signal from the external controller. In other aspects, the source of the applied voltage may be an external device controlled by the external controller.

0042In some aspects, a DAS <b>100</b> can use donor remote units <b>104</b> for communication with base stations without using a direct connection between a master unit <b>102</b> and one or more base stations <b>114</b>. For example, a DAS <b>100</b> may include multiple donor remote units <b>104</b> that can communicate with base stations <b>116</b> via a wireless RF communication link or other suitable wireless link. Such a configuration can be used for a DAS <b>100</b> servicing a coverage area in which a preferable location to receive RF signals from one base station is different from a preferable location to receive RF signals from a different base station. Such a configuration can also be used for a DAS <b>100</b> using n×n multiple-input and multiple-output (“MIMO”) systems, in which n donor remote units <b>104</b> can be positioned at different locations for receiving MIMO signals with sufficient spatial diversity. Using donor remote units <b>104</b> for communication with base stations <b>116</b> rather than using a direct connection between a master unit <b>102</b> and base stations <b>114</b> can extend coverage for public safety communication systems or other telecommunication systems having reduced capacity (i.e., fewer available channels and/or frequency bands).

0043In additional or alternative aspects, the donor remote unit <b>104</b> can be used to increase the reliability of coverage provided by a DAS <b>100</b>. For example, a base station <b>114</b> connected to the master unit <b>102</b> may experience a malfunction that prevents or degrades signal coverage provided by the base station <b>114</b>. A malfunction can be caused by events such as construction or other operations causing a cable link to be severed, an equipment failure in the base station <b>114</b>, etc.

0044In a non-limiting example, a DAS <b>100</b> can have a standard operation mode in the absence of a base station malfunction and an auxiliary mode of operation in the presence of a base station malfunction. In the standard operation mode, the donor remote unit <b>104</b> can be configured to receive downlink signals from the master unit <b>102</b> and to ignore downlink signal traffic from a neighboring base station <b>116</b>. In the auxiliary mode, the donor remote unit <b>104</b> can be configured to establish a communication link with the neighboring base station <b>116</b> for receiving downlink traffic. Establishing such a communication link with the neighboring base station <b>116</b> can reduce or prevent interruptions of at least some telecommunication services in the coverage area of the DAS <b>100</b>. For example, some telecommunications services (e.g., normal voice calls, etc.) provided by the base station <b>114</b> may be interrupted by a malfunction with respect to the base station <b>114</b>. The auxiliary mode can be used to provide a subset of telecommunication services (e.g., public safety services) that can be accessed via the neighboring base station <b>116</b>.

0045<figref idref="DRAWINGS">FIG. 5</figref> is a flow chart depicting a process <b>500</b> for using the donor remote unit <b>104</b> to compensate for a base station malfunction according to one aspect. The process <b>500</b> is described with respect to the system depicted in <figref idref="DRAWINGS">FIG. 1</figref>. Other implementations, however, are possible.

0046The process <b>500</b> involves determining that a malfunction has occurred with respect to a base station <b>114</b> in communication with a master unit <b>102</b> of a DAS <b>100</b>, as depicted at block <b>510</b>. In some aspects, the master unit <b>102</b> can determine that a malfunction has occurred based on a loss of communication with the base station <b>114</b>. In one non-limiting example, the master unit <b>102</b> can determine that the malfunction has occurred based on an absence of downlink traffic from the base station <b>114</b> for an amount of time exceeding a threshold amount of time. In another non-limiting example, the master unit <b>102</b> can determine that the malfunction has occurred based on a failure of the base station <b>114</b> to respond to signaling or other control communications from the master unit <b>102</b> that are used for establishing or maintaining a communication link between the base station <b>114</b> and the master unit <b>102</b>.

0047In some aspects, one or more devices in the DAS <b>100</b> can provide a notification that the base station <b>114</b> is malfunctioning. For example, one or more of the master unit <b>102</b> or the donor remote unit <b>104</b> can generate an alarm notification in response to the donor remote unit <b>104</b> being used to provide signal coverage in the DAS <b>100</b>. Non-limiting examples of such an alarm notification include a data message transmitted to a communication device or outputted in a graphical interface, an audible indicator generated by one or more of the master unit <b>102</b> or the donor remote unit <b>104</b>, a visual indicator (e.g., a flashing light) generated by one or more of the master unit <b>102</b> or the donor remote unit <b>104</b>, etc.

0048The process <b>500</b> also involves configuring one or more remote units to identify a neighboring base station near a coverage area of the DAS <b>100</b> by scanning downlink frequency bands, as depicted at block <b>520</b>. For example, a DAS <b>100</b> may include multiple donor remote units <b>104</b>. A master unit <b>102</b> can respond determining the base station malfunction by providing control signals to the multiple donor remote units <b>104</b> to search for neighboring base stations <b>116</b>. A neighboring base station can include any base station from which signals having specified signal criteria can be received by one or more donor remote units <b>104</b>. For each donor remote unit <b>104</b> that receives the control signal from the master unit, a respective processor <b>204</b> can generate an additional control signal that instructs a respective transceiver <b>202</b> to scan one or more frequency bands for downlink signals or other signals that are transmitted by a base station <b>116</b>. The transceiver <b>202</b> can be tuned or otherwise configured to receive signals in one or more frequency bands specified by the control signal. The processor <b>204</b> can analyze signal traffic in the one or more scanned frequency bands to identify one or more frequencies used by the base station <b>116</b> to transmit downlink signals.

0049The process <b>500</b> also involves selecting at least one of the remote units as a donor remote unit based on the selected remote unit receiving downlink signals from the neighboring base station that meet a specified signal criteria, as depicted at block <b>530</b>. For example, at least two donor remote units <b>104</b> may be within transmission range of a neighboring base station <b>116</b>. One of the donor remote units <b>104</b> may receive signals from the neighboring base station <b>116</b> that satisfy the signal criteria and the other donor remote unit <b>104</b> may receive signals from the neighboring base station <b>116</b> that fail to satisfy the signal criteria. Non-limiting examples of satisfying the signal criteria include as exceeding a threshold signal level, having noise below a threshold noise level or satisfying another quality parameter, etc. The master unit <b>102</b> or another control device in the DAS <b>100</b> can select the donor remote unit <b>104</b> that receives signals from the neighboring base station <b>116</b> that satisfy the signal criteria to establish a communication link with the neighboring base station <b>118</b>. The donor remote unit <b>104</b> that receives signals from the neighboring base station <b>116</b> failing to satisfy the signal criteria can be used to communicate signals with terminal devices in the coverage area of the DAS <b>100</b>.

0050The process <b>500</b> also involves configuring the selected remote unit to establish a communication link with the neighboring base station <b>116</b>, as depicted at block <b>540</b>. For example, a selected donor remote unit <b>104</b> can configure its transceiver <b>202</b> to receive downlink signals transmitted by the neighboring base station <b>116</b> and to transmit uplink signals received from the master unit <b>102</b> to the neighboring base station <b>116</b>.

0051The process <b>500</b> also involves configuring the DAS <b>100</b> to provide signals received from the neighboring base station <b>116</b> to the other remote units in the DAS <b>100</b>, as depicted at block <b>550</b>. In some aspects, the master unit <b>102</b> can be configured in the auxiliary mode to utilize the signals received from the donor remote unit <b>104</b> as downlink signals. The master unit <b>102</b> can process the signals received from the donor remote unit <b>104</b> in the same manner that the master unit <b>102</b> would process signals received from the base station <b>114</b>. The master unit <b>102</b> can provide the signal received from the donor remote unit <b>104</b> to one or more remote units <b>106</b><i>a</i>, <b>106</b><i>b. </i>

0052In additional or alternative aspects, an extension unit <b>103</b> in communication with the donor remote unit <b>104</b> can be used to provide the donor signal to one or more remote units that are communicatively coupled to the extension unit <b>103</b>.

0053The process <b>500</b> also involves determining that the malfunction of the base station <b>114</b> has ceased, as depicted at block <b>560</b>. For example, the master unit <b>102</b> can determine that the malfunction has ceased based on receiving downlink traffic from the base station <b>114</b> or receiving other signal traffic from the base station <b>114</b>.

0054The process <b>500</b> also involves configuring the donor remote unit <b>104</b> to terminate the communication link with the neighboring base station <b>118</b> in response to determining that the malfunction has ceased, as depicted at block <b>570</b>. For example, a control signal can be provided to the donor remote unit <b>104</b> that is selected to receive signals from the base station <b>116</b> in auxiliary mode. The control signal can notify the donor remote unit <b>104</b> to switch from auxiliary mode to standard operation mode. The processor <b>204</b> of the donor remote unit <b>104</b> can respond to the control signal by configuring the transceiver <b>202</b> to cease communicating signals with the base station <b>116</b>.

0055In some aspects, the DAS <b>100</b> can automatically switch to an auxiliary mode. In other aspects, the DAS <b>100</b> can be switched to an auxiliary mode by an operator performing one or more operations to reconfigure one or more of the master unit <b>102</b> and the donor remote units <b>104</b>.

0056In additional or alternative aspects, remote units can be configured to provide device-to-device communication between terminal devices. For example, <figref idref="DRAWINGS">FIG. 6</figref> is a block diagram depicting an example of a remote unit <b>602</b> configured for device-to-device communication according to one aspect. The remote unit <b>602</b> depicted in <figref idref="DRAWINGS">FIG. 6</figref> can be included in the DAS <b>100</b> and can be communicatively coupled to the master unit <b>102</b> or the extension unit <b>103</b>.

0057The remote unit <b>602</b> can include a processor <b>608</b> configured to execute a suitable algorithm for determining whether to switch between a transmit mode to a receive mode. The remote unit <b>602</b> can also include a transceiver <b>604</b> that has a switching module <b>606</b> for switching the remote unit <b>602</b> between a transmit mode for transmitting device-to-device and a receive mode. The switching module <b>606</b> can include one or more switches that can be configured by the transceiver in response to control signals received from the processor <b>608</b>. The remote unit <b>602</b> can also include a signal processing module <b>610</b> that can perform one or more signal processing functions, as previously described with respect to the signal processing module <b>208</b> in <figref idref="DRAWINGS">FIG. 2</figref>.

0058In some aspects, the device-to-device communication can involve a simplex operation (e.g., push-to-talk). In some aspects, the device-to-device communication can be a duplex operation.

0059In the simplex case, at least one remote unit <b>602</b> can be set to a “receive” mode for receiving signals from a first terminal device and at least one additional remote unit <b>602</b> can be set to a “transmit” mode for transmitting signals to a second terminal device. One or more remote units <b>602</b> near a transmitting terminal device can be set to a receive mode for receiving signals from the terminal device. Other remote units <b>602</b> that are further from the transmitting terminal device can be set to a transmit mode for transmitting the signals to a receiving terminal devices.

0060In some aspects, a remote unit <b>602</b> can switch between a transmit mode and a receive mode based on a signal level of signals received from a transmitting terminal device. For a received signal level above a threshold, a remote unit <b>602</b> can switch to a receive mode. For a received signal level below a threshold, the remote unit <b>602</b> can switch to a transmit mode. In additional or alternative aspects, signals received at multiple remote units <b>602</b> from a terminal device can be analyzed to estimate or otherwise determine a geographic location of the terminal device. One or more remote units <b>602</b> can be identified as being located at less than at a threshold distance from the geographic location of the terminal device. The one or more remote units <b>602</b> located at less than a threshold distance from the terminal device can switch to a receive mode.

0061In some aspects, the remote units <b>602</b> can switch from a device-to-device mode to a standard operation mode in the absence of device-to-device communication. A standard operation mode can include the remote units <b>602</b> transmitting uplink signals received from terminal devices to master units <b>102</b> of the DAS <b>100</b>. For example, if all simplex terminal devices in a DAS <b>100</b> are idle, all remote units <b>602</b> can switch to a standard operation mode.

0062In some aspects, a master unit <b>102</b> can coordinate device-to-device communication via multiple remote units <b>602</b>. When a terminal device starts to transmit within the DAS <b>100</b> coverage area, one or more remote units <b>602</b> can receive the signal from the terminal device. The master unit <b>102</b> can monitor signals received by the remote units <b>602</b>. The master unit <b>102</b> can detect that a received signal from a given remote unit <b>602</b> has a signal level above a minimum defined level (e.g., an un-squelch threshold). The master unit <b>102</b> can combine a signal having a signal level above the threshold that is received from a remote unit <b>602</b> with other signals having signal levels above the threshold that are received from other remote units <b>602</b>. For example, received signals having signals above the threshold can be added together into a composite sum. The combined signal can be transmitted to remote units <b>602</b> that are not receiving the signal above the threshold.

0063In some aspects, a terminal device can move between different coverage zones serviced by different remote units <b>602</b>. As the transmitting device moves, a signal level of a signal transmitted by the terminal device may rise above and fall below a specified threshold at different remote units <b>602</b>. If a signal level for a given remote unit <b>602</b> falls below the threshold, the master unit <b>102</b> can exclude or otherwise omit that signal from the summing operation. The master unit <b>102</b> can configure the remote unit <b>602</b> to switch from a receive mode to a transmit mode. The transceiver <b>604</b> of the remote unit <b>602</b> can be switched to a transmit mode for transmitting the newly reconfigured summed signal. Conversely, if a signal level for a given remote unit <b>602</b> rises above the threshold, the master unit <b>102</b> can add that signal to the summing operation. The master unit <b>102</b> can configure the remote unit <b>602</b> to switch from a transmit mode to a receive mode.

0064The master unit <b>102</b> can configure the remote unit <b>602</b> by transmitting control signals to a remote unit <b>602</b>. The processor <b>608</b> can configure the transceiver <b>604</b> in response to the control signals. For example, if a master unit <b>102</b> determines that the remote unit <b>602</b> is receiving signals having signal levels above the threshold signal level (e.g., as a result of a simplex terminal device being keyed), the master unit <b>102</b> can provide a control signal that instructs the remote unit <b>602</b> to switch to a transmit mode. The transceiver <b>604</b> of the remote unit <b>602</b> can be switched to the transmit mode by the processor <b>608</b> in response to the control signal. If the master unit <b>102</b> determines that the remote unit <b>602</b> is receiving signals having signal levels below the threshold signal level (e.g., as a result of a simplex terminal device being un-keyed), the master unit <b>102</b> can provide an additional control signal that instructs the remote unit <b>602</b> to switch from the transmit mode to a receive mode. The transceiver <b>604</b> of the remote unit <b>602</b> can be switched to the receive mode by the processor <b>608</b> in response to the additional control signal.

0065In some aspects, a remote unit <b>602</b> may be configured to transmit signals and receive signals on the same frequency. The remote unit <b>602</b> can distinguish between signals received from a terminal device and signals transmitted by the remote unit <b>602</b> itself by adding a frequency shift to the signals transmitted by the remote unit <b>602</b>. The frequency shift can de-correlate signals transmitted by the remote unit <b>602</b> from signals received from the terminal device. A received signal received from a terminal device can be distinguished from the signals that are transmitted by the remote unit.

0066In some aspects, one or more signals received by a remote unit configured for device-to-device communication can be transmitted to a base station or other telecommunication device via the master unit <b>102</b>. For example, a master unit <b>102</b> can be communicatively coupled to one or more other DAS's. One or more signals received by a remote unit configured for device-to-device communication can communicated to other remote units <b>602</b> and to the master unit <b>102</b> that is communicatively coupled to the one or more other DAS's.

0067The foregoing description of the examples, including illustrated examples, of the invention has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art without departing from the scope of this invention. The illustrative examples described above are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts.